Embodiments described below relate to process field devices. In particular, the embodiments relate to loop current regulators in in process environments.
Process field devices are used in industrial process control systems to monitor and/or control industrial processes. A control device is a process field device which is used to control the process. Example control devices include pumps, valves, actuators, solenoids, motors, mixers, agitators, breakers, crushers, rollers, mills, ball millers, kneaders, filters, blenders, cyclones, centrifuges, towers, dryers, conveyors, separators, elevators, hoists, heaters, coolers, and other such equipment. A process transmitter is a process field device which is used to sense (or monitor) operation of the process, for example by monitoring a process variable such as temperature, pressure, flow, etc. The monitored process variable is transmitted so that it can be used by other equipment in the process, for example by a central control room.
Two-wire process field devices receive power from and communicate over a two-wire process control loop. One standard type of two-wire process control loop uses a 4-20 mA current level on the control loop to represent a process variable or a state of a control device. In such a configuration, a field device can control the current level to a value, such as 10 mA, which is representative of a sensed process variable such as pressure. In other embodiments, digital values are encoded on the two-wire loop using a communication standard such as the HART® communication protocol, Fieldbus or Profibus, for example
In order to reduce the amount of wiring required to couple to a process field device, many process field devices are entirely powered with power received from the two-wire process control loop. Thus, the total amount of power available to the process field device is limited. For example, in a 4-20 mA current loop, the total power available is limited by the lowest level at which the current level can be set (for example 3.6 mA) and the maximum voltage drop available across the device (for example something less than 24 volts in an intrinsic safe location). This is less than 0.09 watts of available power for the device.
In many cases, the functionality of a process device is limited by the amount of power available on the two-wire process control loop. For example, additional functionality may require addition computational capabilities from a microprocessor. This increased computational power requires greater electrical power and may exceed the power budget available from the loop. In order to increase the amount of power available to circuitry in a process field device, field devices typically utilize highly efficient power supplies to convert power received from the two-wire process control loop into a regulated voltage level for use by internal circuitry. One type of power supply, the switching regulator, has been used in process field devices due to its efficiency in providing a regulated supply voltage to the components of the device.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.